Wet Oxidation
Wet oxidation is used for growing thicker (> 100 nm) layers of silicon dioxide for applications such as isolation (field oxides and local oxidation) and dopant diffusion barriers, in which oxide quality is less important.
There are three (3) popular methods of Wet Oxidation:
| Option | Advantages | Disadvantages |
|---|---|---|
| Flash Vaporizer Oxidation | Good for thick and thin oxides, good uniformity. | Cost |
| Pyrogenic Oxidation | Inexpensive, clean, all-gas system, good uniformity | Not suitable for thick oxides because of torch burn. Incurs hydrogen's safety risks. |
| DI Water Bubbler Oxidation | Moderate price, acceptable uniformity for thick oxides | Thin oxides have non-uniformity issues. Cool water vapor causes temperature disturbances. Slower since process gas is only half steam. |
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Typical Film Thickness:
- 500 nm at 1,000 °C (flat) using DI water method
- < 50 nm at 1,000 (flat) using pyrogenic method
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Maximum Film Thickness:
- 20 μm at 1,000 °C (flat) using DI water bubbler
- 3 μm at 1,000 °C (flat) using pyrogenic method
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Batch Size:
- 100 in 18 flat zone
- 200 in 34 heater
- Oxidation Rate: Standard Chart Rates Deal-Grove for both methods
- Oxidation Gases: Hydrogen/Oxygen (Pyrogenic only), DI H2O Steam
- Oxidation Temperature: 800 - 1250 °C
- Refraction Index: 1.4 - 1.47
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Uniformity
- < 3% 1σ at thickness < 2000 Å
- < 2% 1σ at thickness > 2000 Å
Applications: optical waveguides, insulation, isolation (field oxides and local oxidation), dopant diffusion barriers
Record-Setting 30 µm SiO2 Oxidation
Silicon dioxide (SiO2) serves as the primary cladding and buffer layer in silicon-based photonics, isolating the high-index core (e.g., Si or Si3N4) from the substrate. To prevent light leakage (evanescent coupling) into the substrate, especially in mid-infrared or high-power applications, a very thick, high-uniformity oxide layer is necessary. Tystar’s thick optical-grade SiO2 oxidation, achieving a world record setting at 30 µm, provides superior cladding for waveguides, isolating light paths and minimizing crosstalk in silicon photonics platforms. This is crucial for hybrid silicon-silicon nitride platforms, enhancing functionalities like optical signal processing. Notably, researchers at Caltech have leveraged Tystar’s SiO2 oxidation capabilities to achieve world record quality factors (Q ∼ 109) in optical resonators, as reported in Nature Photonics[1].
References
[1] H. Lee, et al., “Chemically etched ultrahigh-Q wedge-resonator on a silicon chip,” Nature Pho-tonics, vol. 6, pp. 369-373, 2012.
